When an oil well is completed after a borehole has been drilled from the earth's surface into a producing formation it is normally necessary to suspend a string of tubing in the borehole so that production fluid is conveyed from the formation to the earth's surface where it can be processed into a lubricating oil, gasoline, diesel fuel and other products that are indispensable for life on the earth as we know it.
Most oil wells include a surface casing on which a wellhead is mounted and a system must be provided in conjunction with the wellhead for suspending tubing in the borehole. Tubing is always suspended, that is, it is never placed in the borehole and the weight of the tubing string allowed to rest on the lower end of the tubing string. For this reason, the mechanism which must support the weight of a long tubing string, frequently exceeding a mile in length, must be carefully designed and constructed.
In the past a typical means of suspending tubing in a wellhead has been by the use of tapered jaws that fit inside an internally tapered body. The jaws have gripping surfaces that when forced by the tapered surface of the tubing hanger into the exterior of the tubing grip the tubing with sufficient strength to suspend it in a bore hole. While this well known system works satisfactorily, it has disadvantages. In recent years, a technique in which a threaded fitting is secured to the upper end of the tubing and the fitting itself is releasably locked into a wellhead has come into use. It is to this latter type of tubing suspension system that this invention is directed.
For background information relating to weliheads and systems for suspending tubing, reference can be had to the following previously issued United States patents:
______________________________________ U.S. PAT. NO. INVENTOR TITLE ______________________________________ Kinzbach7 Casing Head 2,157,964 Tubing Hanger 3,255,823 Orienting and Locking Conductor 4,541 ,490 Adapter For A Wellhead 4,646,827 Tubing Anchor Assembly 4,936,382 Drive Pipe Adaptor 5,092,400 Coiled Tubing Hanger 5,507,349 Downhole Coiled Tubing Latch 5,522,464 Hydraulic Tubing Head Assembly 5,544,706 Retrievable Sealing Plug Coil Tubing Suspension Device ______________________________________